We live in Tulsa, OK, so if you are coming through us, here are some thigns you'll pass along the way up to Chicago:
Grant's Farm--St Louis, MO. free and tons to do!
Meramec Caverns in MO--a lot of fun for kids to see the different rock formations
L. Ingalls Wilder Museum and house-Mansfield, MO--This is about 1hour off the track you'll probably take, but if she like LIW, this is great!
Discoveryland-Sand Springs/Tulsa-Outdoor musical performance of Oklahoma! It has real horses, buggies etc. You'd have to check times for shows.
Black Wall Street/Greenwood in Tulsa OK. Site of the major 1921 Race Riot--the largest in the USA. The Greenwood Cultural Center has some interesting information and you can tour a home from that time. Should be free,but have to schedule tour in advance. There is also Rudisill Library with a lot of info on the Race Riot, and the new John Hope Franklin Center for Reconciliation which has a nice memorial park.
Precious Moments Chapel--Carthage MO
Askinsosie Chocolate Factory--Springfield MO. Single source chocolate. They give free tours and it's fun to watch! Chocolate is expensive though.
McAlester, OK--has some good Italian restaurants (although one is a greasy spoon).
Will Rogers Museum-Claremore and Oologah, OK.
Five Civilized Tribes Museum-Muskogee, OK. Museum on the Five Native American Tribes sent to OK during the trail of tears and now the official "Five Civilized Tribes" of the US.
I don';t think you'll go through Oklahoma City, but if you do, there are some great museums and the OKC Bombing memorial which is very moving.